An offshore platform, often referred to as an oil platform or an oil rig, is a large structure used in offshore drilling to house workers and machinery needed to drill wells in the ocean bed, extract oil and/or natural gas, process the produced fluids, and ship or pipe them to shore. Depending on the circumstances, the platform may be fixed to the ocean floor, may consist of an artificial island, or may float.
Remote subsea wells may also be connected to a platform by flow lines and by umbilical connections. These subsea solutions may consist of single wells or of a manifold center for multiple wells.
FIG. 1 shows a deep sea drilling rig 100 on an ocean surface 105 that processes oil and/or gas 110 obtained from below an ocean floor 115 via a blowout preventer (BOP) stack 120 and a riser assembly 125.
FIG. 2 illustrates a deep sea drilling rig 100′ after exploding due to a defective BOP stack 120′, causing an oil and/or gas spill 210 that pollutes the ocean and needs to be contained. The explosion may further cause the riser assembly 125 to break into portions 125′ and 125″.
The Deepwater Horizon oil spill, also called the BP oil spill, the Gulf of Mexico oil spill or the Macondo blowout, was a massive oil spill in the Gulf of Mexico, and is considered the largest offshore spill to ever occur in U.S. history. The spill stemmed from a sea floor oil gusher that started with an oil well blowout on Apr. 20, 2010. The blowout caused a catastrophic explosion on the Deepwater Horizon offshore oil drilling platform that was situated about 40 miles (64 km) southeast of the Louisiana coast in the Macondo Prospect oil field. The explosion killed 11 platform workers and injured 17 others. Another 98 people survived without serious physical injury.
Although numerous crews worked to block off bays and estuaries, using anchored barriers, floating containment booms, and sand-filled barricades along shorelines, the oil spill resulted in an environmental disaster characterized by petroleum toxicity and oxygen depletion, thus damaging the Gulf of Mexico fishing industry, the Gulf Coast tourism industry, and the habitat of hundreds of bird species, fish and other wildlife. A variety of ongoing efforts, both short and long term, were made to contain the leak and stop spilling additional oil into the Gulf, without immediate success.
After the Deepwater Horizon drilling rig explosion on Apr. 20, 2010, a BOP should have activated itself automatically to avoid an oil spill in the Gulf of Mexico. The oil spill originated from a deepwater oil well 5,000 feet (1,500 m) below the ocean surface. A BOP is a large valve that has a variety of ways to choke off the flow of oil from a gushing oil well. If underground pressure forces oil or gas into the wellbore, operators can close the valve remotely (usually via hydraulic actuators) to forestall a blowout, and regain control of the wellbore. Once this is accomplished, often the drilling mud density within the hole can be increased until adequate fluid pressure is placed on the influx zone, and the BOP can be opened for operations to resume. The purpose of BOPs is to end oil gushers, which are dangerous and costly.
Underwater robots were sent to manually activate the Deepwater Horizon's BOP without success. BP representatives suggested that the BOP may have suffered a hydraulic leak. However, X-ray imaging of the BOP showed that the BOP's internal valves were partially closed and were restricting the flow of oil. Whether the valves closed automatically during the explosion or were shut manually by remotely operated vehicle work is unknown.
BOPs come in a variety of styles, sizes and pressure ratings, and usually several individual units compose a BOP stack. The BOP stack used for the Deepwater Horizon is quite large, consisting of a five-story-tall, 300-ton series of oil well control devices.
The amount of oil that was discharged after the Deepwater Horizon drilling rig explosion is estimated to have ranged from 12,000 to 100,000 barrels (500,000 to 4,200,000 gallons) per day. The volume of oil flowing from the blown-out well was estimated at 12,000 to 19,000 barrels (500,000 to 800,000 gallons) per day, which had amounted to between 440,000 and 700,000 barrels (18,000,000 and 29,000,000 gallons). In any case, an oil slick resulted that covered a surface area of over 2,500 square miles (6,500 km2). Scientists had also discovered immense underwater plumes of oil not visible from the surface.
Various solutions have been attempted to control or stop an undersea oil and/or gas spill. One solution is to use a heavy (e.g., over 100 tons) container dome over an oil well leak and pipe the oil to a storage vessel on the ocean surface. However, this solution has failed in the past due to hydrate crystals, which form when gas combines with cold water, blocking up a steel canopy at the top of the dome. Thus, excess buoyancy of the crystals clogged the opening at the top of the dome where the riser was to be connected.
Another solution is to attempt to shut down the well completely using a technique called “top kill”. This solution involves pumping heavy drilling fluids into the defective BOP, causing the flow of oil from the well to be restricted, which then may be sealed permanently with cement. However, this solution has not been successful in the past.
It would be desirable to have a method and apparatus readily available to successfully contain oil and/or gas spewing from a defective BOP stack, until an alternate means is made available to permanently cap or bypass the oil and/or gas spill, or to repair/replace the defective BOP stack.